Methylxanthines modulate adenosine release from slices of cerebral cortex

Area of Science:

• Neuroscience
• Neurochemistry

Background:

• Adenosine and GABA are key neurotransmitters in the cerebral cortex.
• Methylxanthines are known to affect neurotransmitter release.
• Understanding factors influencing purine release is crucial for neurological research.

Purpose of the Study:

• To investigate the factors affecting the release of purines and GABA from the cerebral cortex.
• To determine the specific influence of methylxanthines on purine and GABA release.
• To explore the underlying mechanisms of purine release, potentially involving a positive feedback system.

Main Methods:

• Incubation of mouse or rat cerebral cortex slices with radiolabeled adenosine, adenine, and GABA.
• Induction of release using ouabain or p-hydroxymercuribenzoate.
• Administration of various compounds including methylxanthines (caffeine, theophylline, aminophylline, IBMX) and non-xanthine phosphodiesterase inhibitors.
• Analysis of the effects on purine and GABA release.

Main Results:

• Ouabain and p-hydroxymercuribenzoate induced purine and GABA release, but ethacrynic acid, phenytoin, noradrenaline, and SC 13504 did not.
• Methylxanthines (caffeine, theophylline, aminophylline, IBMX) at 10(-3) and 10(-4) M significantly inhibited ouabain-evoked purine release.
• Non-xanthine phosphodiesterase inhibitors showed weaker effects on purine release.
• Methylxanthines did not significantly affect GABA release.

Conclusions:

• Purine release is likely not mediated by inhibition of (Na+, K+) ATPase or Mg2+-ATPase.
• Methylxanthines inhibit purine release, potentially through a positive feedback system where adenosine activates adenylate cyclase, increasing cyclic AMP.
• An intracellular receptor for methylxanthines directly inhibiting purine release cannot be excluded.